Four acid phosphatases were isolated from normal human lungs, spleens, kidneys and bladders, and their structural and functional properties were compared with that of human malignant prostatic acid phosphatase. These acid phosphatases possess different molecular weights, amino acid compositions, peptide maps, substrate specificity and optimal pH, although they share at least one common antigenic determinant in addition to their own specific sites. The antigenic structure of human prostatic acid phosphatases (PAP) was analyzed by using three partial tryptic peptide fragments. The entire PAP molecule comprises a minimum of four distinguishable, non-overlapping antigenic determinants. A glycoprotein exhibiting immunological and enzymatic activities of human prostatic acid phosphatase has been purified and amino-terminal sequences of both prostatic acid phosphatase and glycoprotein were found to be different. The primary structure information of protein is very important in elucidating the fundamental biological function. The collaborative research of protein sequencing provides accurate information that can be used for cloning and identification of eukaryotic genes.